Japanese Laid-Open Patent Publication No. 2008-256899 discloses a lens barrel including: a first cylindrical member having a helicoidal screw groove portion and a groove portion in the circumferential direction that continues from the helicoidal screw groove portion on an inner circumference thereof; and a second cylindrical member having, on an outer circumference thereof, a helicoidal screw thread portion that is screwed onto the helicoidal screw groove portion and engages the groove portion in the circumferential direction. With such lens barrel, to increase the mechanical strength even when the cylindrical members receive a force in the optical axis direction, a reinforcing member of a different material to the member that constructs the helicoidal screw thread portion of the second cylindrical member is provided on part of the helicoidal screw thread portion.